Plot of the change in radius of the minority atom on alloying RA − rA versus RA/RB for 181 MgCu2-type compounds. rA is the radius of the A atom in the structure and is calculated from the lattice parameter as 31/2a/8. The points can be fitted to the equation RA − rA = −1.587 + 1.534(RA/RB) − 0.168(RA/RB)2. A systematic deviation is observed for the points at the end of the line as in the case of the AuCu3-type compounds in Fig. 9. RA − rA is almost zero when RA/RB ≃ 1.2, close to the internal radius ratio of 1.225 proposed by Laves (1966).